Gas ignitor



Aug. 28, 1962 J. M. HOFF 3,051,862

GAS IGNITOR Filed Feb. 10, 1960 FIG. 1

GAS BURNER INVENTOR.

JOHN M. HOFF @Mn, 5W

ATTORNEYS United States Patent Office 3,051,862 Patented Aug. 28, 19623,051,862 GAS IGNITOR John M. Hofi, Mansfield, Ohio, assignor to TheTappan Company, Mansfield, Ohio, a corporation of Ohio Filed Feb. 10,1960, Ser. No. 7,827 3 Claims. (Cl. 313-146) This invention relates toan improved electrode device for electric spark ignition of combustiblegases, such as the gas-air mixtures used in domestic gas range burners,associated pilot burners and the like.

It is a primary object of the invention to provide an ignitor of thisclass which will operate efliciently at substantially lower voltage andcurrent values than has commonly been thought necessary for the purpose,whereby the new ignitor is both more economical than conventionaldevices and safer in operation.

Another object is to provide such an ignitor having a very long servicelife, this characteristic resulting from a special feature ofconstruction which affords compensation for the electrode erosion andloss which inevitably occurs.

Other objects and advantages of the present invention will becomeapparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims, the following description andthe annexed drawing setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of but afew of the various ways in which the principle of the invention may beemployed.

In said annexed drawing:

FIG. 1 is a diagrammatic view of a gas burner assembly, such as found ina domestic gas range, including an electric ignitor in accordance withthe present invention;

FIG. 2 is an axial cross-section of the ignitor on an enlarged scale;

FIG. 3 is a similar section at right angles to the section shown in FIG.2; and

FIG. 4 is an end view of the ignitor.

Referring now to the drawings in detail, the gas burner showndiagrammatically in FIG. 1 is a conventional oven burner of a domesticgas range having a series of ports along the bottom thereof for issue ofthe usual combustible mixture of gas and air supplied to such a burner.Beneath this oven burner, adjacent one end of the same, there is a pilotburner 11 which is again of conventional form and adapted to be suppliedwith the same gaseous mixture. An electric ignitor, designated generallyby reference numeral 12, is here associated with the pilot burner 11 forcontrolled ignition of the gas-air mixture issuing therefrom when thesupply of the mixture is established to the same, and the resultingpilot flame, of course, is used to ignite the main or oven burner.

This ignitor comprises a tubular housing 13, which has been made ofstainless steel, with one end thereof flared to form a mouth 14 ofconical section. As will appear more clearly below, the housing forms anouter electrode, and there is an inner electrode 15 in spaced relationwithin the housing. Such inner electrode is in the form of a wire ofsmall cross-section and high electrical resistance extending generallyalong the axis of the housing 13 and being coiled into a plurality ofturns 16 in the region of the housing just behind or .the rear of themouth 14. The terminal portion 15 of the wire electrode at this end ofthe ignitor projects into the mouth 14 and extends interiorlythereacross at a considerable angle to the axis, with the extreme end ortip in close-spaced opposition to the conical inner surface of themouth.

The wire electrode is bare and its turns 16 accordingly spaced apart andnon-contacting.

At its other end, which is within the housing 13, the wire electrode 15is bonded to a conductor 17 which projects from the rear end of thehousing. Excluding the mouth 14, the space within the housing 13 andsurrounding the enclosed portions of the wire electrode 15 and conductor17 is filled with suitable thermal and electrical insulation 18. Afiller of granular magnesium oxide has been used for the purpose, andthe material is firm- 1y packed in the housing for support of the innerelectrode and connected conductor therewithin.

A terminal strip 19 is suitably bonded to the project ing end of theconductor 17 and, as shown in FIG. 1, a wire connects this terminal toone side of the secondary winding of a step-up transformer 20, while theother side of such secondary winding is connected by 'a wire to thehousing or outer electrode. The primary of this transformer is adaptedto be connected to a conventional source of supply, and I have shown asimple switch 21 in the supply circuit to the transformer for control ofthe ignitor. Basically, the operation involves applying, by means ofsuch transformer, high voltage at low current to the electrodes tocreate a spark therebetween effective to ignite the gas-air mixturesupplied to the pilot burner 11, with the raw gas issuing from suchburner being caused at least in part to flow over the mouth of theignitor. The physical arrangement of the components may vary, but it isdesirable to locate the ignitor so as to be in the stream of the raw gasto be ignited and yet not in the flame produced. For example, a relativepositioning as shown will protect the ignitor from flame damage byvirtue of the normal updraft resulting by combustion and correspondingdirection of the flame.

For a number of reasons, it is significant that the inner electrode ofthe new ignitor is in the form of a wire of small cross-section; as amore specific example, this electrode has been made of nichrome wire of.032 inch diameter. Such dimensioning provides a highly concentratedspark and, since the wire electrode has such little mass, the flow ofthe gaseous mixture to the region of the spark is practicallyunobstructed. Moreover, heat is not readily conducted away from the tipof the wire electrode, as would be the case with a fairly heavyelectrode, and such tip actually glows and promotes ignition on suchaccount.

By virtue of these characteristics, it has been found that the newignitor will operate properly, as compared to conventional devices onthe same order, at considerably reduced voltage and current values. Forexample, whereas an ordinary spark ignitor may require 5,000 volts at.013 ampere, an ignitor constructed as aforesaid and including a wireelectrode of the type and size specifically set forth will function witha supply of 2,000 volts at .008 ampere. The electrode gap in the newignitor will generally be on the order of from .020 to .060 inch.

The end portion 15 of the wire electrode will in time become shortenedby inevitable loss of metal, and the turns or coils 16 provide forlengthening the electrode to make up such loss. That is, the turnsconstitute, in effect, storage of the wire and, when the gap hasincreased to a point where loss of the spark cannot adequately becorrected by bending the initial exposed end length of the wireelectrode, the wire is simply pulled from the insulative packing toextend the end turn until the initial exposed length is re-established.The encircling nature of the outer electrode, of course, facilitatespositioning of the tip of the wire electrode, and the relatively largearea of the surface available for the spark also keeps this electrodecool as a result of conductive dissipation of heat therein at the regionof the spark, with deterioration of this electrode being negligible forpractical purposes.

As workers in the art will appreciate, a typical gas cooking ovenassembly in which the ignitor may be used will include various controlsof known design and function for regulation, and possibly programming,of the oven operation. While these are not necessary to the presentinvention, it may be noted that the pilot burner will desira-biyincorporate a flame control of suitable type to prevent the flow of gasto the oven burner when the pilot is cold, or in other words, untilafter the pilot flame has been established by ignition. The ignitorenergization should preferably be maintained for a definite interval toinsure ignition, and the switch controlling the same can be of a typewhich will open only after a time delay for automatic provision of thisfeature.

Other modes of applying the principle of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims or the equivalent of suchbe employed.

I, therefore, particularly point out and distinctly claim as myinvention:

1. An electric spark ignitor for gaseous fuel burning devices,comprising an outer electrode in the form of a tube having a flaredmouth at one end, an inner electrode in spaced relation within saidouter electrode, said inner electrode being made of wire of smallcross-section and high electrical resistance, the inner Wire electrodehaving an end portion within the mouth of the outer electrode at asubstantial angle to the wall of the same and with its tip in closedspaced opposition to the inner surface of said wall, thereby to form aspark gap with the outer electrode, the wire inwardly with respect tothe rnouth having a series of spaced storage turns therein, and beingconnected at its removed end to an external conductor, and a compactedmass of particulate thermal and electrical insulation material fillingthe space within the outer electrode about said turns and the extent ofthe wire electrode to the rear of the same, the wire electrode includingthe turns thereof being thus embedded in said material and beingextensible from within the same at the gap-forming end to compensate forconsumption of said wire electrode in use of the ignitor.

2. An electric spark ignitor for gaseous fuel burning devices,comprising a first electrode made of wire of small cross-section andhigh electrical resistance, a second electrode having a surfaceencircling an end position of said first electrode, the thus encircledend portion of the first electrode being at a substantial angle to saidsurface with its tip in close spaced opposition thereto to form a sparkgap with the same, the first electrode wire having a plurality ofstorage turns therein for extension of the same to compensate loss ofmaterial at such spark tip thereof, and a compacted mass of particulatethermal insulation material surrounding such turns and the remote extentof the first electrode, the first electrode including the turns thereofbeing thus embedded in said material and being extensible from withinthe same.

3. An electric spark ignitor for gaseous fuel burning devices,comprising a first electrode made of wire of small crosssection and highelectrical resistance, a second electrode having a surface disposed inclose spaced opposition to an end of said wire to form a spark gaptherewith, said first electrode having a plurality of storage turnsformed therein and a terminal connection at its other end, the turnsproviding for extension of the Wire electrode relative to the terminalconnection thereof to compensate for loss of material at the spark gapend to maintain proper gap dimension, and a compacted mass ofparticulate thermal insulation material surrounding such turns and theremote extent of the first electrode.

References Cited in the file of this patent UNITED STATES PATENTS393,304 Haskins Nov. 20, 1888 895,030 Lang Aug. 4, 1908 1,290,121 DonatJan. 7, 1919 2,241,295 Clark May 6, 1941 2,548,300 Garner Apr. 10, 19512,948,824 Smits Aug. 9, 1960 FOREIGN PATENTS 840,961 France Jan. 28,1939

